This invention relates to dental articulators, and specifically to articulators for use in modeling or simulating the movement of the human jaw.
Dental articulators are used in prosthodontics. The field of fixed prosthodontics generally relates to nonremovable replacements or substitutes for natural teeth, such as bridges and caps. The field of removable prosthodontics includes removable dentures. Dental articulators are used in both fields in making dental prosthesis. One important characteristic of a dental articulator is the ability to closely simulate the actual centric, lateral, and protrusive jaw movements of the patient in order that the prosthodontist may produce a comfortable and effective dental prosthesis.
Several different types of dental articulators are known. One common type of articulator is the axle and track articulator manufactured by Hanau Engineering Company. An axle and track articulator has an upper frame and a lower frame. Slots or tracks on the lower frame carry an axle attached to the upper frame. See, e.g., U.S. Pat. No. 1,733,507 to McCollun. Although axle and track articulators do only a fair job of simulating human jaw movements, they remain in widespread use today because of their simplicity, smoothness of operation, and convenience. Such articulators may be opened fully without separation by simply pivoting the upper frame 180.degree. on the axle.
A second type of articulator is the articulator-condyle, or "arcon" type. Arcon articulators are characterized by a lower frame carrying a pair of condyle balls and an upper frame having guides which receive the condyles and permit the upper frame to pivot and slide on the condyles and more closely simulate human jaw movement. Such arcon articulators are exemplified by U.S. Pat. No. 3,590,487. Major advances have been made in arcon articulator technology to the extent that a patient's jaw movements can now be almost precisely duplicated. See, e.g., U.S. Pat. Nos. 3,452,439; 3,694,919; 3,896,550; 4,034,474; 4,034,475; and 4,209,909, all to Robert L. Lee.
Despite the superiority of arcon articulators in simulating human jaw movement, they have, nevertheless, failed to supplant the Hanau-type axle and track articulators, for several reasons. One of the advantages of an axle and track articulator is that the frames stay together for hinging and tracking movements and they may be opened 180.degree. so that the prosthodontist may work on the tooth models for both the upper and lower jaw from above. By contrast, in most arcon-type articulators, the frames can be separated at any time and condyles completely leave the guide blocks and articulators come apart when the frames are opened more than about 80.degree. to 90.degree..
In the field of removable prosthodontics, manufactured teeth are positioned in a wax base on the articulator. It is common, when using an arcon articulator, for the teeth to lift the guides slightly above the condyles, introducing inaccuracies into the prosthodontic process. The use of springs to bias the guides onto the condyles has been unsatisfactory, because the required spring pressure hinders opening of the articulator.
It is important that the prosthodontist be able to readily and positively align the upper and lower frames of the articulator in the centric position. (The centric position is that position corresponding to a fully retracted and centered lower jaw.) It is also desirable that the articulator return to the centric position of its own accord, except when study of a particular non-centric position is desired, in which case the prosthodontist should be able to either hold that non-centric position or repeatably return the articulator to that position as necessary. At the same time, it is desirable that the articulator be easily opened and closed while maintaining the centric position.
For many of the reasons discussed above, approximately 50% of all dental schools in the United States require dental students to purchase two different articulators: an arcon-type articulator for fixed prosthodontics, and an axle and track articulator for removable prosthodontics.
Some efforts have been made in the prior art to spring-bias articulators into a desired position. An early example is Burch, U.S. Pat. No. 1,080,809. This patent discloses the use of a spring on an axle and slot articulator to bias the articulator into an open centric position.
Various methods have been used in the past to bias arcon-type articulators into centric position and prevent unwanted separation of the condyles from the guides. One such method is a coil spring connecting the upper frame to the lower frame between the condyles. This arrangement has proved unsatisfactory because the spring is extended when the articulator is opened and prevents full opening of the articulator. Moreover, the spring biases the articulator closed, hindering study of hinging motion. Additionally, the spring is bent if the articulator is opened too far. Rubber bands placed between the upper and lower frames between the condyles present similar disadvantages.
Accordingly, an object of the present invention is to provide a means for biasing an articulator into the centric position while permitting free opening and closing of the articulator in that position.
Another object of the present invention is to provide a novel hinge on which an arcon-type articulator can pivot into a fully opened position of at least 180.degree.. Another object is to maintain the guide means in contact with condyle during eccentric movements.
Yet another object of the present invention is to provide a means for holding the articulator in a non-centric position and for repeatably reproducing desired non-centric positions of the articulator.